Q&A: Excavating in Frozen Ground

Q.What’s the most
cost-effective way to thaw a site for excavation? We
are building a 16x24-foot addition with a crawlspace
underneath, and the frost is already 12 inches
deep.

A.Jay Meunier, a
contracting specialist at S.T. Griswold and Co., a
ready-mix supplier in Williston, Vt.,
responds: If your excavation contractor is not
equipped to tackle 12 inches of frost, the next
best alternative, other than waiting until spring,
is to use a ground heater. The rental fee can be
somewhat expensive — about $900 per day in
our area — but ground heaters can remove a
lot of frost in 24 hours over a 1,500-square-foot
area. These units come with a glycol tank and
tubing that is laid on the frozen ground with 12 to
24 inches between tubing runs. The area is then
covered with poly and insulating blankets that
force the heat from the warm glycol and ground
moisture downward, thus thawing the area.

In loamy and sandy soils, it’s common
to thaw 12 inches of frozen ground within 24 hours.
Clay and gravel tend to take longer, but
I’ve been told that you can speed the
process by spraying water on the area before
spreading the poly and blankets.